Litoria larisonans, Purser & Doughty & Rowley & Böhme & Donnellan & Mitchell & Shea & Amey & Mitchell & Catullo, 2025

Litoria larisonans sp. nov.

Figs. 16–18 View FIGURE 16 View FIGURE 17 View FIGURE 18

Suggested common name: Western Desert Tree Frog.

Holotype. WAM R174603 ( Fig. 16 View FIGURE 16 ), calling male from Dale’s Gorge , Karijini National Park , 82.6 km NE Tom Price, WA, Australia (22.4768°S, 118.5629°E), collected by R. Bray, R.J. Teale, L. Umbrello and J. Huey on 14 March 2015. GoogleMaps

Paratypes. ( Fig. 17 View FIGURE 17 ). Five adult females: WAM R117337 , from Hope Downs , 80.5 km NW of Newman, WA, Australia (22.9513°S, 119.0792°E), collected on 7 September 1993 GoogleMaps ; WAM R119287 , from Mileura Station homestead, 118.7 km W of Meekatharra, WA, Australia (26.3667°S, 117.3333°E), collected on 1 December 1993 GoogleMaps ; WAM R114077 , from Kumarina , 149.3 km S of Newman, WA, Australia (24.7°S, 119.6°E), collected on 2 July 1992 GoogleMaps ; WAM R175951 , from Ex-wanna Station , 158.3 km SW of Tom Price, WA, Australia (23.6268°S, 116.6218°E), collected on 2 September 2016 GoogleMaps ; WAM R110776 , from Jimblebar East , 60.8 km E of Newman, WA, Australia (23.4575°S, 120.3225°E), collected on 9 February 2005 GoogleMaps .

Four adult males: WAM R175952 , from Ex-wanna Station , 158.1 km SW of Tom Price, WA, Australia (23.6268°S, 116.6217°E), collected on 2 September 2016 GoogleMaps ; WAM R179352 , from Murrin Murrin mine camp, 56.9 km NE of Leonora, WA, Australia (28.7112°S, 121.8800°E), collected on 15 November 2018 GoogleMaps ; WAM R125748 , from Fortescue River Crossing, 94.9 km S of Karratha, WA, Australia (21.5716°S, 117.0525°E), collected on 24 February 1996 GoogleMaps ; WAM R174492 , from Augustus National Park , 152.5 km SW of Paraburdoo, WA, Australia (24.3634°S, 116.8705°E), collected on 13 August 2014 GoogleMaps .

Material examined. Details of the 33 (17 females and 16 males) L. larisonans sp. nov. vouchered specimens examined are presented in Table 1 View TABLE 1 and tadpoles in Table 6 View TABLE 6 .

Diagnosis. Litoria larisonans sp. nov. is assigned to Litoria based on the presence of a horizontally oriented contracted pupil and the absence of a palpebral reticulum ( Tyler & Davies 1978). Molecular and morphological data indicate that L. larisonans sp. nov. is closely related to L. rubella sensu stricto and exhibits other characters typical of the L. rubella species complex: moderately small size (<50 mm), small head, short and broadly fringed fingers with rudimentary basal webbing, short hindlimbs with partially webbed toes, a dark dorsolateral stripe on the head and body and a high-pitched, multi-pulsed male advertisement call consisting of a single note. Litoria larisonans sp. nov. is morphologically indistinguishable from other taxa in this species complex and must be diagnosed using molecular data. From a genetic perspective, in the mitochondrial ND4 alignment, 21, 19 and 20 sites reliably diagnose L. larisonans sp. nov. from L. capitula , L. pyrina sp. nov. and L. rubella respectively ( Table 3 View TABLE 3 ).

Description of holotype. Adult male ( Fig. 16 View FIGURE 16 ); moderate body size (33.4 mm SUL); body moderately flattened and wide; head small (HDL/SUL = 0.27), flattened (HD/SUL = 0.14), and narrow (HDW/SUL = 0.28); head length equal to width (HDL/HDW = 0.96); snout triangular in dorsal view, tip of snout blunt, rounded in profile; canthus rostralis rounded; loreal region steep, concave when considered in conjunction with upper labial margin; crown of head flat; nares ovate, on anterolateral edge of snout, oriented dorsolaterally; eyes small (EYE/HDL = 0.22), pupils oriented horizontally; eye to naris distance 1.65 X eye diameter; tympanum circular with raised annulus; well-developed supratympanic fold angling posteroventrally towards attachment of arm; tympanum and eye equal in diameter (TMP/EYE = 0.95); arms moderate ([UAL+LAL]/SUL = 0.26), thin; fingers with basal webbing; relative length of fingers I<IV<II<III; tips of fingers with well-developed discs, distinct circumarginal grooves and narrow fringing, discs relatively wide compared to width of the penultimate phalanx (third finger disc width twice finger width); subarticular tubercles rounded; metacarpal tubercles ovate; nuptial pads cover entire basal half of finger I on anterior (inner) surface, continuing on dorsal side only on middle of finger and tapering away from anterior (inner) edge of finger I; hindlimbs short (TIB/SUL = 0.38); relative length of toes I<II<III~V<IV; tips of toes with well-developed discs, distinct circumarginal grooves and narrow fringing; discs slightly smaller than those of fingers (fourth toe disc width 1.9 X toe width); subarticular tubercles distinct, rounded; inner metatarsal tubercle distinct, spatulate; outer metatarsal tubercle absent; toes partially webbed, extending beyond distal tubercle of all toes except IV, webbing extending between distal and penultimate tubercle on toe IV. Skin of dorsal surface smooth, lacking dorsolateral folds, parotoid glands, and ridges; glandular tissue located between mouth and arm; ventral surface of body finely granular, smooth on limbs.

Colour in preservative. Dorsal background colour greyish cream with irregular dark brown blotches. Wide brownish lateral head stripe, beginning on snout and wrapping around nares, continuing along loreal region, through eye and tympanum, angling posteroventrally and terminating behind the arm; between the nares and eye, darker pigment of canthal stripe demarcates loreal region from top of snout; hiatus of pigment on tip of snout forming a V-shape. Ventral surfaces, other than gular region, cream; base colour of gular region and vocal sac stippled with black. Posterior surfaces of thighs lack pattern.

Measurements (mm) of holotype. SUL 33.4, FOL 18.3, TIB 12.7, FEL 12.0, LAL 5.0, UAL 3.7, HDW 9.4, DFE 5.1, IOD 3.0, IND 1.5, HDL 9.0, HD 4.7, SNT 4.2, EN 3.3, NS 0.8, EYE 2.0, TEY 0.9, TMP 1.9, 3TL 8.0, 3FDW 1.4, 3FW 0.7, PL 10.3, 4TDW 1.3, 4TW 0.7, IMT 1.5.

Description. Morphometric characters vary considerably among 17 adult females and 16 adult males ( Table 5 View TABLE 5 ), mostly independent of sex. Females (SUL 28.5–38.8 mm; mean 32.9 mm) tended to be longer than males (SUL 26.2–36.7 mm; mean 32.5 mm) and more rotund when gravid; within sexes body shape varied from gracile to robust depending on body condition. Body width usually wider than head width; body moderately flattened to slightly robust. Annulus of tympanum raised relative to skin of temporal region. Poorly- to well-developed terminal discs on digits; relative width of finger discs 1.5–2.7 greater than finger width, and toe discs 1.1–1.9 greater than toe width, some of which is attributable to artefacts of preservation. Dorsal and ventral skin smooth to granular.

Colour. Colour variation is described from photographs in life of six animals (see Fig. 18 View FIGURE 18 ), the moribund holotype image ( Fig. 16 View FIGURE 16 ) and in situ observations. Dorsal colouration broadly uniform across head, body and outer surface of limbs; across individuals dorsal colouration can be fawn, cream, brown, rich chocolate-brown, red-brown, brick-red or greyish, sometimes whitish during daytime; irregular dark brown pigmentation may be present on dorsal surface and appendages, often forming small specks or marbling, extent highly variable; darker dorsolateral streak occasionally present, generally stronger in inguinal region. Ventral surface uniformly cream, always lighter than dorsal surface; gradual to sharp contrast between dorsal and ventral colouration over dorsolateral region, generally coincides with lateral head stripe when present. Pale patch below eye, variable in lightness and extent among individuals. Distinctly darker lateral stripe originating from a V-shape hiatus on tip of snout, wrapping around nares, passing through eye and tympanum, dissipating variably from above attachment of arm to more posteriorly towards groin, generally more diffuse posteriorly; stripe contrast and intensity varies from well-defined and dark to pale and poorly contrasted. Pale yellow to dull red pigment on posterior of thighs and inguinal region, with dark spots similar to dorsal colouration but no distinct pattern, extent and saturation variable between individuals. Iris golden, copper-brown to reddish-brown. Male gular pigmentation dark brown. Nuptial pads light to dark brown. In preservative, reddish hues over body tend to be lost, colour and contrast of dorsolateral stripe usually fades, colour of thighs tends to be lost, colour of iris lost.

Embryos. Unknown.

Tadpole body and tail shape. Body and tail shape similar to description for L. rubella with mid-dorsal region of body slightly convex in profile, and dorsal fin initially low at its origin over tail/body junction, with a slight dip before rising to maximum height over middle of tail ( Fig. 8H View FIGURE 8 ), as observed in specimens of L. rubella from central Australia.

Tadpole colour in life. Tadpoles collected from Rous Creek and Carnarvon, WA were similar in dorsal, lateral and ventral pigmentation to those of L. rubella (e.g. see Fig. 8E View FIGURE 8 ). One specimen at stage 36 from Carnarvon, WA ( Fig. 8H, I View FIGURE 8 ) was atypically leucistic.

Metamorphs. A sample of four metamorphs from Carnarvon, WA ranged from 17.0–18.0 mm (mean 17.5). Metamorphs are reddish-brown with much reduced or no dark streaks on each side of vertebral region or in each inguinal region ( Fig. 8L View FIGURE 8 ). The iris is coppery red. As in adults, a broad, dark brown lateral stripe extends from snout to groin but the white stripe beneath it from snout to armpit is poorly defined.

Advertisement call. Call descriptions are based on the calls of 14 males ( Table 4 View TABLE 4 , Fig. 5 View FIGURE 5 ). The advertisement call of L. larisonans sp. nov. comprises a single, highly-pulsed note ( Fig. 6 View FIGURE 6 ), sounding like a harsh screech. Individuals had a call duration of 0.56– 1.03 s and 32–66 uniformly spaced pulses, repeated at a rate of 55.7–75.1 pulses/s. The dominant frequency ranged between 1.67–2.24 kHz.

Etymology. The specific name “ larisonans ” (Latin) refers to the gull-like male advertisement call characteristic of the species (ona, “sounds like” and Larus, Latin for gull).

Habitat and ecology. Litoria larisonans sp. nov. are found in a wide range of habitats including woodland, plains, rocky ranges, and deserts from arid inland to coastal regions. It uses large rock crevices, tree hollows and leaf litter for shelter. Males call from the ground, trees, shrubs, or rocky areas besides permanent and ephemeral water sources in both natural and disturbed habitats. In remote arid areas, it is generally confined to ranges or larger watercourses. They are frequently found in sinks, drainpipes and toilets. In hot and dry environments, animals are generally found resting in a water conserving posture with a whitish colouration to reduce cutaneous water loss. Litoria larisonans sp. nov. has been detected calling in all months via the FrogID project, but most records are between November and March. Males are commonly heard calling in disturbed areas, with 21% of FrogID records of the species documented as being in suburban or urban habitats and 26% of records in rural areas. Litoria larisonans sp. nov. breeds primarily in lentic waterbodies, with the majority of FrogID records of this species documented by users as being in flooded areas (26%), small ponds (21%) and large ponds (11%).

Distribution and conservation status. Litoria larisonans sp. nov. is restricted to the western arid zone of WA. The northern extent of its distribution occurs along the southern boundary of the Great Sandy Desert. It occurs to the wEsT Of ThE GibsOn And GREAT VicTORiAn DEsERTs,And nORTh Of AppROximATELy LATiTUdE 29⁰S. NEw RAngE ExTEnsiOns TO ThE south have been recorded every few years over the last 20 years (PD via WA Museum database records, unpublished data). This is a widely distributed species and can be very abundant where it occurs. Although conservation status requires formal assessment, owing to its range size (Extent of Occurrence> 800,000km 2) and absence of obvious threats, it meets the criteria for Least Concern (International Union for Conservation of Nature 2012).

Comparisons with other species. Litoria larisonans sp. nov. is not sympatric with any congeners ( Rowley et al. 2021, Menzies 2006). No morphological or acoustic characters are known to reliably diagnose L. larisonans sp. nov. from the L. rubella population in the Kimberley.